144 ON THE EXTINCT MAMMALIA OF 



The mental foramen is situated below the back part of the first premolar tooth, 

 corresponding also with the back part of the articulation of the symphysis. 



Dentition. — The fossil contains the permanent true molars, and the temporary 

 molars except the first premolar of the lower jaw. The molar series of both jaws are 

 represented in figures 5, 6, plate XIII. Canines appear to have existed in the upper 

 jaw, and they, as well as incisors, probably belonged to the lower jaw. 



A premolar in the upper jaw occupies an advanced position from the others, 

 separated from them by a hiatus of four lines (figure 5). It has a crown twice the 

 breadth of the length inserted by a pair of widely separated and somewhat divergent 

 fangs. The crown is fore-and-aft oblong, with a trenchant lower border becoming 

 slightly more pi'ominent towards the middle. It is worn off internally in a sloping 

 manner from attrition of an opposed tooth below. The latter is lost in the fossil. 



The second and third premolars of both jaws possess great proportionate breadth, 

 and are inserted by widely separated and somewhat divergent fangs. These teeth 

 remind us of the corresponding ones of the eocene Dicliohune cuapidatus. 



The temporary true molars in form and construction hold the same relation to 

 those of the permanent series as in living ruminants. 



The permanent true molars of both jaws have the ordinary constitution of those of 

 ruminants generally. 



The second upper premolar has an oblong crown four times the breadth of its 

 length and thickness. It is thickest posteriorly, and is feebly trilobate externally. 

 The lower border is trenchant and most prominent at the middle. Internally it is 

 worn by attrition in a sloping manner. 



The third upper premolar has an oblong crown three times the breadth of its 

 length. It is trilobate externally, the posterior lol^e forming a transverse angular 

 ridge at the triturating border, and the anterior pair together forming an angular 

 cusp. Internally the crown appears rather trilobed, Avhich, structurally, is really the 

 condition of the crown. The triturating surface is wide clavate in outline, with the 

 back part widest. It presents an exposed tract of dentine crossed hy a transverse 

 angular valley, separating the angular ridge behind from the cusjd in front. 



The upper temporary true molar is a reduced representative of the teeth behind. 

 It is so worn that the enamel of the triturating surface is obliterated except a small 

 crescentic islet intermediate to the posterior pair of constituent lobes. 



The upper permanent true molars have crowns with the breadth of their base a 

 little exceeding the Avidth and length. The first and second of the fossil are fully 

 protruded, and are insei'ted in the usual manner. The last has almost entirel}^ pro- 

 truded, and is slightly worn. 



The crowns have nearlj^ the relative proportions of those in the Camel, though 



